This invention relates in general to control panels, and in particular to graphic display control panels of the type used for displaying or controlling industrial processes or the like.
Control panels designed for monitoring and controlling the operation of complex systems, such as industrial processes or manufacturing systems, are known in the art. These control panels typically include a graphic display which visually simulates the flow path and/or operation of a particular system or process, so that an operator can monitor and control the operation of the system by observing indications appearing on the panel. The control panels may include lamps, annunciators, and other visual or audible signal devices to inform an operator when certain operating conditions, such as the operation of pumps, valves, conveyors, or the like are taking place. The control panels also frequently include switches or similar control input devices, located on the control panel in functional or logical relation to the graphic symbol denoting the controlled function, thereby enabling an operator to control a particular aspect of a system by manipulating the corresponding control device at the control panel.
Such control panels frequently include localized internal illumination to indicate the status of a particular element in the system being controlled. Because industrial systems and processes are frequently modified, necessitating corresponding modifications to the related control panels, it is known to provide the control panels with internal illumination sources that can be readily repositioned at any desired location behind the display panel. One example of such repositionable illumination sources is shown in U.S. Pat. No. 3,624,648 entitled "Graphic Display Annunciator", in which one or more lamps are magnetically attached at any desired position within the display panel. Changes in the underlying system or process are readily accommodated, simply by changing the graphic symbols on the display panel and by quickly repositioning the magnetically-mounted lamps disposed behind the display panel.
More recently, it has been proposed to mount control switches or similar actuators within the control panel and behind the display panel. The switches or actuators, as well as illumination sources denoting various process or system functions, may be mounted by magnetic or other means for ease of repositioning. The switches within the control panel are operated through the display panel by the presence of an operator's finger or by an actuating device, at or adjacent the control panel immediately in front of the behind-panel switch. Further details of within-panel switches or control actuators are found in copending patent application Ser. No. 967,111 filed Dec. 7, 1978.
While the internal mounting of indicators and control switches within a control panel enables more rapid modification of the process or system representation of the panel, and is generally more economical to manufacture because the front display panel need not be penetrated for installing switches or indicators, the physical presence of switches or indicators behind the display panel has heretofore interfered with attempts to back-light the display panel. Panel back-lighting in the past has been provided, if at all, simply by mounting one or more lamps immediately behind the display panel, casting a relatively uniform illumination over the entire panel. The ideal effect, as viewed from the front of the display panel, is a relatively diffused illumination emanating from the display panel, except as those locations where graphics deliberately obscured the illumination. However, with control panels having internally-mounted switches or indicators of the types illustrated in the foregoing patent and pending application, the physical presence of the internal devices (and the signal or control lines connected to such devices within the control panel) causes shadows to be cast on the internally-illuminated control panel. Those shadows are not only unsightly as seen from the front of the panel, but may actually detract from operator comprehension of the process or system graphically depicted on the panel.
Consequently, there is a need for a control panel which can be uniformly back-lighted, without sacrificing the advantages of indicators or control elements positioned behind the front display of the control panel.